Identifying Antistreptokinase Antibodies
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An accelerated dose tissue plasminogen activator (tPA) reduces mortality in acute myocardial infarction as compared with streptokinase (SK). Streptokinase is antigenic and will lead to the development of neutralising antibodies that have the potential to limit the effectiveness of repeat SK therapy. Accordingly, tPA is frequently administered to patients with recurrent infarction after SK treatment. Alternatively, one could identify those with high antibody titres and selectively use tPA when resistance was present.
To determine the marginal cost-effectiveness of various thrombolytic strategies in patients with prior acute myocardial infarction (AMI), including the identification of patients with resistance to SK, using point-of-care testing.
A decision analytical model was used to compare three strategies: repeat SK therapy, tPA to all, or selective tPA use for SK resistance identified using point-of-care testing. The perspective for analysis was that of a Canadian provincial (Ontario) Ministry of Health. Only healthcare costs directly incurred by the insurer were included. Short-term costs were obtained for treatment of AMI and complications. Potential benefits from treatment were estimated only with respect to survival, and are calculated as the additional life-years from the continuing survival of persons who would have died in the first few weeks after AMI but were spared. An incremental cost-effectiveness ratio (CER) was computed as the ratio of these incremental costs and benefits. Therefore, the marginal cost-effectiveness represents dollars (1999 Canadian) per additional short-term (5–6 weeks) survivor.
The use of tPA in all patients with prior AMI resulted in the greatest mortality reduction, whereas the selective use of tPA for those with resistance had the most favourable CER. The selective use of tPA is a cost-effective strategy, with CERs varying from $Can85 964 when 5% are resistant to $Can72 100 when 95% are resistant. The CER improves with increasing levels of resistance. Although more expensive, the administration of tPA to all patients with prior AMI remains cost-effective even when levels of resistance are as low as 5%.
In patients with a prior MI and possible resistance to SK, the use of tPA, whether selectively based on antistreptokinase antibody status or simply given to all, is cost-effective.
KeywordsAcute Myocardial Infarction Streptokinase Thrombolytic Agent Acute Myocardial Infarction Patient Anisoylated Plasminogen Streptokinase Activator Complex
The authors have provided no information on sources of funding or on conflicts of interest directly relevant to the content of this study.
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